Question

The following PHP example code only works if the “bar” elements come before the “foo” elements. If they are in the wrong order, I will get a “call to a member function on a non-object” error.

$data = array();
foreach($elems as $e) {
  if($e['type'] == "foo") {
    $data[$e["key"]->foo_data($e["data_foo"]);
  }
  elseif($e['type'] == "bar") {
    $data[$e["key"]] = new Bar($e);
  }
}

My solution at the moment is to iterate twice through $elems. Another solution would be to use usort with a custom sort function that puts “bar” elements before “foo” elements.

Are there any programming patterns or libraries that would allow me to process the elements in arbitrary order?

Answer 1

Looping twice seems like the most sensible solution. Loop once to prepare your objects, loop a second time to let those objects process data. There may be an entirely different, better solution, but that’s hard to say without seeing a more concrete use case.